33 Impacts of seaborne trade on coal importing countries global summary Impacts

33 impacts of seaborne trade on coal importing

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33 Impacts of seaborne trade on coal importing countries – global summary Impacts of changing the quality of coal due to importing
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One of the most important aspects of moisture content is the effect on NOx production. Research by Ikeda and others (2003) in Japan raised concerns about the impact of the increasing use of Indonesian subbituminous coals in boilers designed with advanced low NOx burners. They found that subbituminous blends with bituminous coals showed evidence of elevated unburnt carbon in the ash and higher NOx production, based on experimentation in a pulverised fuel test furnace with a fuel rate of just 0.1 t/h. The results showed that the blend of coals produced more undesirable effects than when each coal was burned separately; the use of the blend resulted in increased NOx emissions and unburnt carbon in fly ash as the concentration of subbituminous increased. However, adaptation of the secondary air flow angle reduced these effects to enable a higher proportion of subbituminous coal to be burned. Most bituminous coals that are traded internationally contain some 12–15% moisture ( see Table 3); moisture levels of some Indonesian coals can be well over 20% ( see Table 4), similar to levels seen in PRB coals in the USA. Consequently, a switch to these low sulphur, but higher moisture coals require careful blending and testing in the power stations to determine the correct adaptations to ensure there is minimal or no loss in efficiency or availability. Gunderson and others (1994, 1996) noted that when some US utilities increased the quantity of PRB coals, the subbituminous coals tended to suppress the pulveriser mill outlet temperature. Attempts to attenuate the temperature increased the parasitic load on the plant and resulted in derating of the plant. However, there were no detrimental effects on burner flame stability despite the higher reactivity of the subbituminous coal. Test burns of blends of subbituminous and bituminous coals at the Gibson plant, Illinois, also resulted in a reduction in the mill outlet temperature and a loss in boiler efficiency (Meehan and others, 1995). 8.3 Chlorine content A literature study carried out by Tillman and others (2009) established the effects of corrosion and ash deposition on a boiler when blending high chlorine solid fuels into the normal coal feed. The analysis relied heavily on papers published throughout the 1990s when much of the material came out. The conclusions highlighted the wealth of knowledge regarding the effects of chlorine content of solid fuels, its sources, and reactions in pulverised fuel firing. Yet, the research over the years was not considered exhaustive with plenty of scope for further work. Chlorine is an increasing problem in pulverised fuel combustion with the rising use of different rank coals, but also with the increasing importance of cofiring (sustainable) fuels such as biomass.
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